The criticism spiked after the U.S. Chemical Safety Board offered a dim glimpse into the plant, which did not have sprinkler systems, stored chemicals in combustible wooden buildings and was not required to follow a fire code.

Rafael Moure-Eraso, chairman of the safety board, one of several agencies investigating the explosion, said standards for regulating reactive chemicals have “many large holes.”

Minutes after the testimony, Boxer demanded a more precise timeline for action from EPA safety official Barry Breen.

“EPA has to step up to the plate and do a lot more,” said Boxer, the committee's chair. She repeatedly dismissed Breen's testimony as defensive, vague and without urgency, and pledged to take her concerns to the White House.

Breen tried to appease the committee. “I need to find a way to convey to you our sense of urgency,” he said in the same calm voice, but was interrupted as Boxer continued to lay out her demands.

Her criticism centered on the agency's lack of regulatory initiative. The last safety warning issued on ammonium nitrate, the chemical that detonated the West plant, is 16 years old. The EPA last issued a national alert about chemical safety in 2007.

“Lives are being lost and recommendations were made a long time ago, and nothing's happening,” Boxer said.

She called on the EPA to adopt a 2002 proposal based on the safety board's warning on reactive chemicals. The group said then that federal regulations fail to address “the hazards from combinations of chemicals and process-specific conditions” in individual plants.

“We're going to work with you, and if we have to, against you, to get this done,” she said before she cut off the hearing for a Senate vote on immigration.

“In order to establish that time frame, we need to understand the issue better, so that's what we're doing now,” Breen said.

A federal-state investigative team announced last month that it could not determine what caused the blast, and the safety board has yet to release its full findings. Last month, the board blamed the Bureau of Alcohol, Tobacco, Firearms and Explosives and Texas regulators for the delay, accusing them of blocking its access to witnesses.